1. Field of the Invention
The present invention relates to a multi-layer substrate and a method for producing the multi-layer substrate. More specifically, the present invention relates to a multi-layer substrate having a structure in which both principal surfaces of a core substrate on which surface mount devices are mounted are sealed with sealing resin layers, and to a method for producing the multi-layer substrate.
2. Description of the Related Art
As one multi-layer substrate, a multi-layer substrate having a structure such as that shown in FIG. 14 is proposed. As shown in FIG. 14, the multi-layer substrate includes a core substrate (ceramic multi-layer substrate) including a plurality of laminated ceramic layers. An active chip component 140, such as a semiconductor device, is disposed on one of principal surfaces of the core substrate 110, and a passive chip component 150, such as a capacitor, is disposed on the other principal surface of the core substrate 110.
Sealing resin layers 120 and 130 are formed on the corresponding principal surfaces of the core substrate (ceramic multi-layer substrate) 110. A surface electrode 121 and a via conductor 122 are formed on a lower surface of the resin layer 130.
As with this multi-layer substrate, in a multi-layer substrate having a structure in which the sealing layers 120 and 130 seal the corresponding principal surfaces of the core substrate (ceramic multi-layer substrate) 110, the core substrate 110 is warped due to a difference between the expansion/contraction coefficient of the core substrate 110 and the expansion/contraction coefficient of the resin layer 120 and the expansion/contraction coefficient of the core substrate 110 and the expansion/contraction coefficient of the resin layer 130 in a resin curing step when forming the resin layers 120 and 130. This reduces the reliability with which a multi-layer substrate is mounted on, for example, a module substrate, and, depending upon the circumstances, causes disconnection of a conductor provided on the multi-layer substrate.
Thermal stress between the core substrate 110 and the resin layer 120 and between the core substrate 110 and the resin layer 130 may cause peeling between the core substrate 110 and the resin layer 120 and the core substrate 110 and the resin layer 130.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2009-188218